Hydraulic fracturing is a process in which an underground geologic formation that is disposed adjacent to a bore hole is fractured by injecting a pressurized material in order to extract a desired substance, such as oil and/or a gas (such as natural gas), from the geologic formation. The injection of the pressurized material creates channels, i.e., fractures, in the geologic formation through which the desired substance may flow to the bore hole and be retrieved. In this process, the material injected into the geologic formation is often a liquid carrying solid particles that are often referred to as a proppant. The proppant migrates into the fractures that are formed and holds them open so that the desired material can flow out of the fracture. A problem that has been encountered in many instances, however, is that the proppant flows back into the bore hole after the pressure is relieved, which allows the fracture to close, thereby reducing the efficiency of the process.
Therefore, in many hydraulic fracturing processes, the proppant is mixed with a tacky resin, such as a polyamide resin, and this mixture is injected into the bore hole. The tacky resin coats the proppant particles and facilitates adhesion of the particles to each other so that when the mixture flows into a fracture, the proppant particles bind together. This makes the proppant more efficient in keeping fractures open after the injection pressure is eliminated, as compared to uncoated proppant particles.
A drawback to such a procedure, however, has been that the tacky resin must be transported to the well site, stored at the well site in storage tanks, and mixed with the proppant at the well head at the time of use. Moreover, the tacky resin tends to stick to equipment, such as mixers and piping. These drawbacks lead to significant capital equipment costs and production inefficiencies.
As a result, it would be desirable to provide improved coated particles that can be used, for example, as a proppant in hydraulic fracturing.